Green roofs good for environment

The city’s energy provider is making green roofs its top priority.
Researchers at Columbia University have found that green roofs like the one atop a Con Edison building in Long Island City can be a cost-effective way of improving the city’s environment.
The Green Roof, which is home to 21,000 plants on a quarter-acre of the company’s Learning Center roof, keeps water from running into sewer systems and causing overflows. The roof retains 30 percent of the rainwater that falls on it, which is then released as vapor by the plants.
Stuart Gaffin, a research scientist at Columbia’s Center for Climate Systems, said the city has a combined sewer system that carries both storm water and wastewater. During heavy rains, the system reaches capacity and discharges a mix of water and sewage into New York Harbor, the Hudson River, the East River and other waterways.
According to Gaffin, if the city’s one billion square feet of roofs were transformed into green roofs, it would be possible to keep more than 10 billion gallons of water a year out of the city sewer system.
Researchers used instrumentation to measure sunlight entering and leaving the green roof. That data allowed them to calculate the amount of energy leaving the roof in the form of water vapor. The study concluded that, based on the cost of building and maintaining a green roof, it costs as little as 2 cents a year to capture each gallon of water.
“The information we are collecting from Con Edison’s roofs is invaluable in helping us determine the costs and benefits of green infrastructure projects,” said Gaffin. “Without solid data from experiments like this, it is impossible for us to know which projects are the best options for protecting the environment.”
Con Edison built the green roof and formed its research partnership with Columbia in 2008, with the expressed purpose of using it as an outdoor laboratory for environmental research. Through the partnership, Gaffin’s team and Con Edison officials found that green roofs and white roofs save energy and reduce urban air temperatures.
“When we built our green roof, we were confident that researchers from Columbia would gain important knowledge about protecting the environment,” said Saddie Smith, vice president for facilities at Con Edison. “Three years later, it’s clear that our project has helped us understand how roofs can save energy, cool the atmosphere and prevent storm water runoff.”